EMBRYOLOGY OF CRYPTOBRANCHUS 553 



ence: in these latter forms the female, not the male, cares for 

 the eggs. 



The egg capsules of the urodeles, as in other groups, show 

 generic and even specific differences (e.g., the specific differences 

 in the egg masses of Amblystoma, Smith '11 b). This is what 

 might be expected, since the capsules are the product of the soma, 

 not of the germ cells ; the facts are in no way incompatible with 

 von Baer's law. The close resemblance between the egg envel- 

 opes of Cryptobranchus and Amphiuma accords with the sys- 

 tematic relationship. Amongst terrestrial urodeles there is no 

 close approach to the type found in Cryptobranchus; but in 

 general we should seek for affinities in forms having the egg 

 capsules more or less independent in the cluster, connected by 

 stalks (e.g., as in Desmognathus, Wilder '99), rather than in 

 forms in which the individual capsules are surrounded by a com- 

 mon jelly mass, as in Amblystoma. 



The origin of the follicle cells of Cryptobranchus has been 

 traced (Part I) from the epithelial cells of the ovarian wall. 

 Hence these cells belong to the soma, and the rather marked 

 differences between the follicle cells of Cryptobranchus and 

 Necturus are of value for comparison only with a very limited 

 range of forms. 



Taking up the history of the egg proper, we first note that 

 the progressive change of the ovarian egg from analecithal through 

 an isolecithal to a telolecithal stage is a recapitulation of a very 

 ancient series of events in the phylogeny. The actual amount 

 of yolk present is a coenogenetic character, for the yolk content 

 changes greatly within nearly related forms. 



The factors that determine the amount of yolk present in the 

 eggs of different species are complex and do not readily fall under 

 any single law. Protection of the eggs through nesting and 

 brooding habits makes possible a reduction in their number, 

 enabling the female to endow each egg with a larger store of 

 yolk, thereby giving the young a better start in life. Such a 

 store of yolk allows development to go further before the young 

 animal is cast upon its own resources, so that the necessity for 

 peculiarly larval adaptations is minimized. In purely terrestrial 



JOURNAL OF MOBPHOLOGY. VOL. 23, NO 3 



